We demonstrate that the work function of a metal gate can be vaned by inserting a very thin metal layer ("Metal A") between a thick metal ("Metal B") and the gate dielectric. The flat band voltage (VpB) of the MOS (metaloxide-semiconductor) capacitor structure can he controlled within the range bounded by Metal A and Metal B individually, as demonstrated with various stacked bimetal layers. For continuous thin layers, we speculate that the work function tunability may be due to the drastic change of the electron density in the thin continuous metal layer in direct contact with a bulk metal. This drastic change of electron density results in a larger junction depth than that expected for B bulk metal. Non-uniform thin layers also appear effective for workfunction tuning as well, and the observed VFB shift is attributed to the metal island formation at the dielectnc/Metal A interface. IntroductionConventional poly Si gate technology has faced several challenging issues due to poly-depletion and B penetration. Recently, the "dual metal gate" approach has attracted attention to improve CMOS performance, as opposed to mid-gap metals, such as TiN and TaN. For CMOS integration, metals with "tunable" workfunctions may be suitable for metal gate applications. Various alloy systems, such as metal alloys (RufTa)[l], silicides (NiSi)[2] and nitndes (MoN)[3], have been investigated for work function "tunability". Both alloying and implantation are being considered as possible techniques to tune the metal gate work function.Recently, another approach has been suggested by several groups using stacked metal layers as the electrode for a MOS (metal-oxide-semiconductor) system for tuning the flat band voltage (work function). Ciao et al. reported work function tuning of a dual metal gate stack using AVTaN bimetal layers deposited by sputtering [4]. Olsen et al. have also demonstrated work function tunability of 0.1V by changing the TaN thickness from 40A to 808, in the TdTaN/HfO2/Si MOS structure. [5] In this work, we systematically examine the workfunction tunability of bilayer metal gate electrodes. ExperimentalA schematic cross-sectional view of OUI capacitors is shown in Fig. 1. The gate metal stack consists of a very thin bottom metal layer on the gate dielectric (Metal A) and a thick capping metal layer (Metal B). The thickness of Metal A was vaned in the target range of 58, to IOOA, utilizing a quartz-crystal microbalance that intercepted the flux in theebeam deposition chamber. A stacked MOS capacitor was fabricated to obtain the flat hand voltage (VFB) behavior. The bi-metal/Si02/Si MOS structure was fabricated in the following sequential manner. A gate dielectric (44 8, thick thermal Si02 film) was formed on HF-last prepared, n-type Si(100) (I-IOOcm). The bimetal layers were then sequentially deposited by e-beam evaporation, without breaking vacuum, and with no intentional substrate heating in order to minimize interfacial alloying between the metals. The pressure was maintained at 6 -8~1 0 .~ Torr during deposition an...

We have studied the magnetoresistance (MR) of locally modified Cu(20 nm)/AlOx(1 nm)/NiFe(20 nm)/AlOx(1 nm)/Cu(3 nm) on a Si substrate. The local modification was performed by irradiating Cu ion beams on a photoresist wire-covered film. After irradiation, the hysteresis loop shows step-like behavior at a specific ion dose, which is caused by the difference in the switching fields of the irradiated and unirradiated region of the film. Because of this, plateau-like behavior is observed in the transverse MR measurement of the film with 1 × 1016 ions/cm2. A cross-sectional transmission electron microscopy image shows the irradiation induced intermixing of the magnetic layer with nonmagnetic layers.

Various chemical compounds contribute to the naturally pleasant flavor of milk. Over time, however, and with unwanted chemical reactions, loss of flavor is inevitable. This study was conducted to identify and quantify volatile flavor compounds associated with off-flavored and commercial reduced-fat milk products. Fresh milk was used for the preparation of altered milk samples having off-flavors such as "light-oxidized" and "highacid." Milk lacking freshness (i.e., milk produced two weeks before sampling and maintained at 40oF in the dark) also was compared with fresh unaltered milk and two commercial milk samples. For headspace analysis, milk samples were subjected to SPME-GC for volatile compound identification. In addition, the composition and aerobic and coliform microbial counts for all milk samples were analyzed. The milk samples did not differ in the concentrations of volatile flavor constituents. When comparing "light-oxidized" milk samples (200 lx exposure for 1 or 3 hr), 2-butanone and pentanal concentrations tended to increase as light exposure time increased. All milk samples had similar fat and total solids contents. "High-acid" milk had a greater total aerobic microbe count than the other milk samples. Fresh milk had a greater octanal concentration than the offflavored reduced-fat milk samples did. This might indicate that octanal is an important contributor to fresh milk flavor and deserves further study